The present invention relates to power supply, and in particular, to power supply to process a semiconductor wafer and a semiconductor making apparatus and a semiconductor fabricating method using the same.
Etching systems using plasma have been used in various fields and include an electron cyclotron resonance (ECR) etching system. In the ECR etching system, by applying a direct current (dc) flows to a coil disposed on an outer surface of a vacuum chamber or container, a magnetic field is generated, and a high voltage is applied to a magnetron to start oscillation. This introduces a microwave into the vacuum chamber to resultantly generate plasma therein. Ions incident to a sample are accelerated by applying a bias voltage of an alternating current (ac) to a sample stage. To electrostatically adsorb the sample, a dc bias voltage is also applied to the sample stage.
Power supply to produce a direct current to generate a magnetic field, power supply to produce a dc voltage to generate a microwave or to supply a dc bias voltage, and power supply to produce ac power for an ac bias voltage have been used as described above.
FIG. 6 shows high-frequency power supply for a semiconductor making apparatus of the prior art in a block diagram. In FIG. 6, high-frequency power supply produces high-frequency power to apply an ac bias voltage to a sample stage as a load to accelerate ions incident to a sample on the sample stage. A power directional coupler 41 senses strength of the power to output a power sense signal according to the strength. A controller 42 calculates a power amplification factor according to a difference between a power setting value as a preset value of strength of power outputted from a control microcomputer 1 of the semiconductor making apparatus to the high-frequency power supply 4 and a power sense value fed from the power directional coupler 41. A fixed oscillator circuit 43 outputs a fundamental wave fixed to a predetermined frequency of the high-frequency power supply 4. An amplifier 44 amplifies, according to the power amplification factor from the controller 42, the fundamental wave outputted from the oscillator circuit 43 to output a desired high-frequency power. The control microcomputer 1 of the semiconductor making apparatus outputs the power setting value to the high-frequency power supply 4 and also monitors the power sense value.
FIG. 7 shows dc power supply for a semiconductor making apparatus of the prior art in a block diagram. In FIG. 7, dc power supply 5 applies a dc current to a coil as a load to generate a desired magnetic field. A current sensor 51 senses strength of the dc current to output a dc sense signal according to the strength. A controller 52 outputs, according to a difference between a current setting value outputted from the control microcomputer 1 of the semiconductor making apparatus and the current sense value fed from the current sensor 51, a duty ratio of a switching unit 53, namely, a ratio of an on time of the switching unit 53 to one period of operation. A voltage transformer 54 including a primary side connected to a switching device 53 and a dc voltage supply 55 to supply a predetermined dc voltage to the primary side. The switching device 53 turns on and off according to the duty ratio from the controller 52 to chop the dc voltage. The chopped dc voltage is transformed to be outputted from a secondary side of the voltage transformer 54. A smoothing device 56 smoothes the output voltage from the secondary side of the transformer 54 into a dc voltage such that the dc power supply 5 resultantly outputs a desired direct current. The control microcomputer 1 of the semiconductor making apparatus outputs the power setting value to the dc power supply 5 and also monitors the current sense value. Description has been given of dc power supply to output a dc current. This similarly applies to dc power supply which receives a voltage setting value from the control microcomputer 1 to output a dc current. For example, the dc power supply is used to apply a dc voltage bias to a sample stage for the electrostatic adsorption the wafer. In this case, a voltage sensor which senses strength of the output voltage to output a voltage sense signal according to the strength is used in place of the current sensor 51.
In general, in a part of a control block such as the controller 42, the amplifier, or the power directional coupler 41 of FIG. 6 constituting a closed-loop control system such as the high-frequency power supply and the dc power supply described above, when an offset appears in an input to output relationship due to aging of analog parts and/or a latch-up phenomenon of digital parts of the control block, an unexpected change or shift also occurs in its control variable according to the offset. This is because the offset of the input to output relationship in the part of a control block of the closed-loop control system reflects in the power sense value of FIG. 6 such that the controller 42 sets the power amplifier degree to equalize the power sense value to the power setting value. For example, when the power amplifier degree to equalize the power sense value to the power setting value, actual power differs from the power setting value by the offset. Even if the control microcomputer 1 is monitoring to determine whether or not the power sense value is within a predetermined allowed range of the power setting value, since the power sense value is already equal to the power setting value, the control microcomputer 1 cannot detect occurrence of the abnormal offset and hence determines that the situation is normal. This also applies to the dc power supply of FIG. 7. Assume, for example, that an unexpected offset occurs in the input to output relationship of the current sensor 51. For example, when the current sense value is equal to the current setting value by controlling the duty ratio, actual power differs from the target value by the offset. However, the control microcomputer 1 cannot detect occurrence of the abnormal offset and hence determines that the situation is normal.
As a result, although the operation is achieved according to the predetermined setting value, the system cannot detect any fault during the semiconductor wafer fabrication. Until a defect of a semiconductor wafer thus processed is detected in a process downstream the fabrication process, the semiconductor wafers with the defect are continuously fabricated in each lot unit including, for example, 25 semiconductor wafers. This possibly leads to loss of a large amount of money. The diameter of the semiconductor wafer and the value added to the semiconductor wafer are increasing today. Therefore, potential of the loss due to defects in lot unit is increasing. In the field of semiconductor making apparatuses, a need exists for higher precision of the output power from these power supplies. This reduces the allowed range of only explicit abnormalities of constituent components but also a fine offset value due to gradual aging or the like. It is therefore important to detect occurrence of a fine offset to prevent defects.
It is therefore an object of the present invention, which has been devised to remove the problems, to provide power supply and a semiconductor making apparatus and a semiconductor wafer fabricating method using the same capable of detecting an abnormal offset due to an abnormality and abnormal aging of parts of power supply, particularly, high-frequency power supply and dc power supply employed in a semiconductor making apparatus.
To achieve the object, the present invention uses devices and steps as below.
According to the present invention, there is provided power supply for receiving a power value setting signal setting strength of power from said power supply and a power on/off instruction to set on or off of the power to produce the power, wherein if a power sense signal according to a value obtained by sensing the strength of the power exceeds a predetermined value when said power on/off instruction is off, the power is suppressed even if the power on/off instruction is subsequently set to on.
Alternatively, there is provided according to the present invention a semiconductor making apparatus comprising a processing chamber for processing a semiconductor wafer, power supply for outputting a current, a voltage, or power necessary for the semiconductor wafer processing, a control microcomputer for setting strength of the power to said power supply and for setting the outputting of the output item to on or off, and output sensing means for sensing the output item and for outputting an output sense signal according to a value obtained by sensing the output item, wherein if the output sense signal exceeds a predetermined threshold value when the outputting of the output item is off, the processing is stopped for a subsequent semiconductor wafer to be processed.
Moreover, there is provided according to the present invention a semiconductor wafer fabricating method comprising the steps of setting, to power supply for supplying a current, a voltage, or power necessary for processing of a semiconductor wafer, strength of the output; setting outputting of the output item to on or off; sensing the output item and for outputting an output sense signal according to a value obtained by sensing the output item; and stopping the processing for a subsequent semiconductor wafer to be processed if the output sense signal exceeds a predetermined threshold value when the outputting of the output item is off in said step of setting the outputting of the output item to on or off.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.